Prospective assessment of a gene signature potentially predictive of clinical benefit in metastatic melanoma patients following MAGE-A3 immunotherapeutic (PREDICT).

BACKGROUND: Genomic profiling of tumor tissue may aid in identifying predictive or prognostic gene signatures (GS) in some cancers. Retrospective gene expression profiling of melanoma and non-small-cell lung cancer led to the characterization of a GS associated with clinical benefit, including improved overall survival (OS), following immunization with the MAGE-A3 immunotherapeutic. The goal of the present study was to prospectively evaluate the predictive value of the previously characterized GS. PATIENTS AND METHODS: An open-label prospective phase II trial ('PREDICT') in patients with MAGE-A3-positive unresectable stage IIIB-C/IV-M1a melanoma. RESULTS: Of 123 subjects who received the MAGE-A3 immunotherapeutic, 71 (58.7%) displayed the predictive GS (GS+). The 1-year OS rate was 83.1%/83.3% in the GS+/GS- populations. The rate of progression-free survival at 12 months was 5.8%/4.1% in GS+/GS- patients. The median time-to-treatment failure was 2.7/2.4 months (GS+/GS-). There was one complete response (GS-) and two partial responses (GS+). The MAGE-A3 immunotherapeutic was similarly immunogenic in both populations and had a clinically acceptable safety profile. CONCLUSION: Treatment of patients with MAGE-A3-positive unresectable stage IIIB-C/IV-M1a melanoma with the MAGE-A3 immunotherapeutic demonstrated an overall 1-year OS rate of 83.5%. GS- and GS+ patients had similar 1-year OS rates, indicating that in this study, GS was not predictive of outcome. Unexpectedly, the objective response rate was lower in this study than in other studies carried out in the same setting with the MAGE-A3 immunotherapeutic. Investigation of a GS to predict clinical benefit to adjuvant MAGE-A3 immunotherapeutic treatment is ongoing in another melanoma study.This study is registered at www.clinicatrials.gov NCT00942162.

Immunochemical characterization of the modulator protein of the ATP,Mg-dependent protein phosphatase.

Polyclonal antibodies raised against the modulator protein of the ATP,Mg-dependent protein phosphatase completely neutralize all known properties of the purified modulator: inhibition or inactivation of the phosphatase catalytic subunit as well as the kinase FA-mediated activation of the ATP,Mg-dependent phosphatase. They do not cross-react with phosphoinhibitor-1 or the phosphatase catalytic subunit. Direct analysis of boiled or unboiled skeletal muscle extracts by Western blotting reveals a 32 kDa polypeptide corresponding to the modulator protein as the most dominant protein staining band.

On the dephosphorylation of the ATP,Mg-dependent protein phosphatase modulator.

The dephosphorylation of the modulator subunit is an essential step in the kinase FA-mediated activation of the ATP,Mg-dependent protein phosphatase. Mg2+ is implicated in this autocatalytic dephosphorylation which is not effected by the addition of phosphoinhibitor-1. Dephosphorylation of free modulator by the catalytic subunit is also largely Mg2+-dependent but can be abolished by phosphoinhibitor-1 in concentrations comparable to the amount of modulator used as substrate (micromolar). The phosphorylase phosphatase activity of the catalytic subunit is inhibited by nanomolar concentrations of phosphoinhibitor-1 and is completely independent of divalent cations.

Interaction of myelin basic protein with the different components of the ATP,Mg-dependent protein phosphatase system.

Myelin basic protein (MBP) reduces the amount of phosphatase activity produced in the kinase FA-mediated activation of the ATP,Mg-dependent phosphatase. MBP was shown not only to inhibit the activated enzyme, but also to impair the kinase FA-mediated activation of the inactive phosphatase. In addition MBP prevents the time-dependent inactivation of the catalytic subunit by the modulator protein. These observations point to a regulatory role for MBP in the reversible activation of the ATP,Mg-dependent protein phosphatase by kinase FA.

The ATP, Mg-dependent phosphatase: role of Mg ions in the expression of the phosphorylase phosphatase activity.

The activation of the ATP, Mg-dependent phosphatase [FCM] by kinase FA has been shown to involve the phosphorylation or thiophosphorylation of the modulator subunit [M] and the consequent isomerization of the catalytic subunit [FC] into the active conformation. The inactive catalytic subunit [free FC] exhibits substantial activity in the presence of non-physiological concentrations of Mn ions whereas the Mn2+-activation of the intact FCM-enzyme requires the proteolytic destruction of the modulator subunit. The present study points to the importance of Mg2+ in the activation of the phosphatase. The inactive catalytic unit can be activated by millimolar concentrations of Mg2+ and the thiophosphorylated FCM-enzyme only expresses its phosphorylase phosphatase activity after a subsequent trypsin treatment in the presence of Mg ions.

Isolation and characterization of two 70 kDa modulator-complexes from rabbit skeletal muscle.

The activation as well as the inactivation of the ATP,Mg-dependent protein phosphatase has been shown to be totally dependent upon the presence of the modulator subunit. This modulator (inhibitor-2) is a heat stable protein and its isolation in pure form (32 kDa) always includes a boiling step. The boiled modulator fractions are known to be inhibitory to the phosphatase activity. Unboiled rabbit skeletal muscle preparations do not contain "free modulator", but two higher molecular weight complexes (70 kDa) can be isolated which have the 32 kDa modulator together with a 38 kDa protein. One complex is the already characterized inactive ATP,Mg-dependent phosphatase [FCM] while the second one, [MX], although seemingly of identical composition, does not exhibit phosphatase activity when measured under the usual conditions. The MX-complex does not inhibit the phosphatase activity unless subjected to a boiling step which dissociates the modulator subunit. The unboiled [MX] exhibits the activation as well as the inactivation characteristics of the free modulator.